Overall objectives: To characterize the molecular organization of lipids and proteins in myelin membranes; and to define the molecular interactions that stabilize the membrane packing in normal myelin and in myelin that has been modified by in vitro chemical treatment or by genetic or pathological conditions. A correlation of biophysical and biochemical techniques (including X-ray diffraction, electron microscopy, SDS-polyacrylamide gel electrophoresis, immunobloting, and thin-layer chromatography) applied to different types of specimens (including whole unfixed or fixed tissue, tissue homogenates, and reconstituted model systems of lipids and proteins) will be used to address the following specific questions: (1) Where are specific lipids and proteins localized in the myelin membrane? The effects of metal cations on the structure of intact myelin will be corrected with their binding to isolated myelin lipids and proteins and to reconstituted multi-layers of lipids and proteins. Changes in myelin composition of neurological mutant mice will be correlated with the structure of myelin membranes in these mutants. (2) What is the structural and chemical basis of the stability of membrane packing in myelin? Myelin fron neurological mutant mice will be surveyed for possible correlations between altered composition and changes in membrane packing. The chemical composition of the nerve sheaths from certain invertebrates and phylogenetically-older vertebrates will be related to the ultrastructure of the membrane assemblies in these sheaths. The dependence of membrane packing on lipid and protein composition will be determined from an analysis of multilayer structure in reconstituted model systems. (3) How do the specialized junctions in the myelin sheath relate to its stability? Attempts will be made to detail the organization and stability of paranodal axo-glial junctions by X-ray diffraction from unfixed nerve regions which are enriched in these structural differentiations of myelin. The meridional diffraction from central nervous system myelin will be analyzed with respect to its possible origins from the tight junctions peculiar to this myelin and from the organization of lipids and proteins in the plane of the myelin membrane.